Core plugs of the type to which the present invention relates are commonly referred to as freeze plugs and may be removed from the associate engine when it is to be stored at subfreezing temperatures. One such prior art freeze plug is described in U.S. Pat. No. 3,361,288. Ordinarily, such a plug cannot be removed from an engine block in which it has been mounted without the plug being destroyed. Also, the amount of expansion of that prior art core plug can vary substantially from one plug to the next wherefore damage to the plug can easily occur during installation thereof by inexperienced personnel.
Removal and replacement of freeze plugs in the engines of boats has been extremely difficult because of the relatively inaccessible location of the plugs on such engines. Therefore, it would be desirable to provide a new and improved freeze plug which could be easily removed without damage from a boat engine or the like